On a sunny day (Tue, 26 Jun 2018 09:15:07 +0100) it happened The Natural
Philosopher  wrote in :

>
>Its all fairly academic. You still have st it up to be on a fixed IP
>address and *mutatis mutandis* it makes little odds whether that is done
>on the router or the Pi itself. It still isn't broadcast and so no one
>knows where to find it unless you run a local name server OR everyone
>has a common host table.

ARP requests are part of the ethernet protocol,
have the requesting party ask for the MAC for a given IP.
The MAC is what is needed to commie-nuke-aid.

If I do  ping 192.168.178.23 from 192.168.178.76
then the folowing commie-nuke-aid-tion will happen on the ethernet LAN:
06/26-12:48:29.207826 ARP who-has 192.168.178.23 tell 192.168.178.76
no reply, as IP ...23 as does not exist,

But if I do  ping 192.168.178.159 from 192.168.178.76
then you get a reply with the MAC, as ...159 does exist:
6/26-12:15:24.294017 ARP who-has 192.168.178.159 tell 192.168.178.76
06/26-12:15:24.294026 ARP reply 192.168.178.159 is-at C8:60:0:2A:85:2C
The MAC of 192.168.178.159 is C8:60:0:2A:85:2C
Now the MAC is used for the rest of the commie-nuke-aid-ion

Raspi at ...76 needs to know the MAC of ...159 so it can send the ping.

So for unknown IP addresses an ARP request is send on the LAN asking for the
MAC of that IP,
and then that MAC is used to commie-nuke-aid.

 https://en.wikipedia.org/wiki/Ethernet_frame

But you guys already know that I suppose.

As to fixed MACs , well I can :- :-) well you can pose as any MAC,
in fact in all the sensors I wrote / designed, I just think of some MAC, as
long as there are not 2 the same on the LAN.
For the outside world
 on the Linksys WiFi routers / access points I have you can set the MAC by
updating firmware and pose as Annie Wan:
 http://panteltje.com/panteltje/wap54g/index.html
Now that was also a thousand years ago,

Nothing is safe in this world.

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